1. Field of the Invention
The present invention relates to the field of filters, and more particularly, to the field of filters for ultraviolet light.
2. Background Information
The use of ultraviolet laser light to ablate material from a workpiece in order to modify the shape of the workpiece is used in a number of fields. In most such systems, a fixed laser pulsed energy results in the ablation of a fixed quantity of material from the workpiece. Typically, a pulsed excimer laser is employed for such ablation processes. These lasers typically emit their laser beam at 193 nm or 248 nm. Since the excimer laser is a pulsed laser, each pulse to which a workpiece is exposed ablates the same quantity of material for a uniform workpiece. Where it is desired to remove a quantity of material which is not an integral multiple of the quantity removed by one pulse, additional control is required. One way of adjusting the amount of material ablated per pulse is to change the beam fluence by changing the laser power. This technique suffers from a variety of disadvantages, including reduction of the power to the point where the beam becomes unstable or non-reproducible. Further, adjustment of the power of the laser is a relatively slow process. Alternatively, a variable beam expander may be employed. However, such expanders are expensive and reduce the collimation of the laser beam. Available commercial ultraviolet light filters Cannot be used to reduce the intensity of the ultraviolet light because the ultraviolet light damages their filter properties.
Consequently, there is a need for an improved technique for adjusting the intensity of ultraviolet light.